1.I am attempting to salvage an old custom power amp that has 6 tube sockets. I would like to use 4 Russian 6P3P-E's (6L6) as the outputs(they are compatible with the iron).
What tube could I use in front of each pair of the outputs,
analogous to the lone 6AN8's used in front of each pair of KT88's in the Dynaco Mark III?

2.Also, an answer to this would be helpful. Are the LTP and CCS circuit enhancements or tube eliminators?

You need to use whatever tubes were intended by the original designer, or equivalents. Alternatively, redesign it to suit your requirements.

LTP (long tail pair) is a sub-circuit, sometimes used as an input stage or phase splitter.

CCS (constant current source) is used for bias or as an active load. I suppose you could regard this as a circuit enhancement, but it is not always possible to simply insert a CCS in an existing circuit.